They're certainly not THE hardest, but the hardest ones for me personally were Harvest Moon for SNES and Valkyrie Profile for PS1. My mom had a heck of a time trying to locate a copy of the former, checking many stores, and I myself struggled to find a copy of the latter. Granted, we weren't trying to get either of these on the actual day of release. Harvest Moon very well could've already been out for a couple months or more, and with Valkyrie Profile, I remember it was about four months past the release date. I called up stores that carried games one by one out of the phone book looking for Valkyrie Profile, and none had any copies except for an independent game store that had one single copy. So I snatched that up immediately.